<template>
    <div class="item-list">
        <div class="item" 
            v-for="item in letters"
            :key="item" 
            :ref="item"
            @click="handleLetterClick"
            @touchstart = "handelTouchStart"
            @touchmove = "handelTouchMove"
            @touchend = "handelTouchEnd"
            >{{item}}</div>
    </div>
</template>

<script>
export default {
    props:{
        cities:{}
    },
    data () {
        return {
            touchStatus:false,
            startY: null,
            timer: null
        }
    },
    computed: {
        letters () {
            const letters = []
            for(let i in this.cities){
                letters.push(i)
            }
            return letters
        }
    },
    updated () {
        this.startY = this.$refs['A'][0].offsetTop
    },
    methods: {
        handleLetterClick(e) {
            this.$emit('change',e.target.innerText)
        },
        handelTouchStart() {
            this.touchStatus = true
        },
        handelTouchMove(e) {
            if (this.touchStatus) {
                if(this.timer) {
                    clearTimeout(this.timer)
                }
                this.timer = setTimeout(()=>{
                    const touchY = e.touches[0].clientY - 79
                    const index = Math.floor((touchY - this.startY) / 20)
                    if (index >= 0 && index < this.letters.length) {
                        this.$emit('change', this.letters[index])
                    }
                },16)
                
            }
        },
        handelTouchEnd() {
            this.touchStatus = false
        }
    }
}
</script>

<style lang="stylus" scoped>
@import '~@/assets/varibles.styl'
    .item-list
        display flex
        flex-direction column
        justify-content: center
        position absolute
        top 1.58rem
        right 0
        bottom 0
        width 0.4rem
        .item
            text-align center
            line-height 0.4rem
            color $bgc
</style>
